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Five desktop quad-core solutions compared


It's a twenty-core rumble
— 1:01 AM on March 5, 2007

AS YOU MAY KNOW, we've already reviewed the top-end desktop quad-core processor rigs from Intel and AMD. We examined the Core 2 Extreme QX6700 upon its debut, and we covered AMD's Quad FX platform even before it hit store shelves. What we found, in a nutshell, is that four processor cores is a wonderful thing to have, but only if you have some heavy multitasking to do or you happen to make extensive use of one of the few applications out there capable of taking full advantage of four cores simultaneously. But things have changed somewhat since our last dance with quad-core systems, and so we're gathered here today to take another look.

Chief among the new developments is the availability of cheaper—err, less expensive—quad-core options like the Core 2 Quad Q6600 and Athlon 64 FX-70. Intel and AMD like to showcase their top performing chips in order to show off what they can do, but top-speed-grade processors are rarely the best values. What's more, we've found that practically any top-speed-grade incarnation of a processor tends to be in a rough spot with respect to heat and power consumption. Lower speed grades promise higher performance per watt.

For instance, the basic power and heat rating, or TDP, of the Core 2 Extreme QX6700 is 130W. Although it's the same technology and runs only 266MHz slower, the Core 2 Quad Q6600's TDP is an Al Gore-approved 105W. Officially, the Athlon 64 FX-70's thermal power rating is the same considerable 125W per chip (in a two-chip solution) as its bigger brother, the FX-74, but we had a hunch the 2.6GHz FX-70 wouldn't be the same class of double-barreled blowtorch as the 3GHz FX-74. There is, of course, one way to find out: test 'em. And so that's what we've done.

We've also recently made the transition to Windows Vista for our test platforms, a move that promises to take better advantage of these quad-core system architectures in various ways. Join us as we fire up our widely multithreaded suite of test applications, many of them 64-bit executables, to see which quad-core solution offers the best mix of price, performance, and energy efficiency.

Four cores, two chips, and how many sockets?
Since we're already reviewed both of these basic technologies, I will spare you most of the gory details here. If you'd like more info on the "Kentsfield" quad-core processors from Intel, go have a look at our Core 2 Extreme QX6700 article. And if you're unfamiliar with AMD's Quad FX platform, you can find our take on it right here. The Cliff's Notes version goes like this: neither of these products feature a truly native quad-core processor. Kentsfield is comprised of two Core 2 Duo chips cuddled up together in a single package. You get four cores in total, but in groups of two—and the two chips have to communicate with one another by means of the system's front-side bus. The great advantage of this scheme is that Core 2 Quad variants can use the same motherboard infrastructure as the Core 2 Duo.


A pair of Athlon 64 FX-70s and the Core 2 Quad Q6600.

Quad FX, meanwhile, uses a variation of the Opteron infrastructure, complete with dual CPU sockets and a pair of dual-core processors, in order to reach four cores in a desktop platform. Quad FX's main concession to desktop use is that it doesn't require registered DIMMs, just run-of-the-mill DDR2 memory. Although it makes for larger, pricier motherboards, Quad FX's dual-socket arrangement arguably offers better integration between two dual-core chips thanks to AMD's HyperTransport interconnect. Because each CPU has dual memory channels hanging off of it, Quad FX also has twice the peak theoretical memory bandwidth of the Core 2 Quad—or more, if you count the Core 2 Quad's front-side bus as the primary constraint.

Making the most of the Quad FX platform's memory architecture, however, can be tricky. Since each CPU has its own integrated memory controller, access to RAM can be very quick, but if CPU 1 has to access data in the memory space controlled by CPU 2, memory access will be considerably slower. Fortunately, Windows Vista incorporates kernel improvements for non-uniform memory access (NUMA) architectures like Quad FX, so testing with this OS ought to let the Quad FX platform put its best foot forward.

As I've mentioned, the Core 2 Quad's motherboard situation is simple: it will work with most newer motherboards intended for the Core 2 Duo. Quad FX's motherboard situation is also simple, but in a different way: you can choose any motherboard you want, so long as it's the Asus L1N64-SLI WS. This beast is indeed a decent enthusiast-class motherboard, but it's a little too, er, enthusiastic for some of us, with a total of four PCIe x16 slots, 12 SATA ports, and dual Nvidia chipsets that draw nearly as much power as a theater screening An Inconvenient Truth. Here's another inconvenient truth: the L1N64-SLI WS costs $350.

That little wrinkle complicates life for the Quad FX platform. AMD has said that more Quad FX motherboards are on the way, but as far as we know, no others are immediately imminent. For now, Quad FX remains tied to one board.

AMD has attempted to keep the price equation in line by selling Quad FX processors at relatively reasonable prices. The original plan was to sell them in pairs at $599 per pair for the FX-70, $799 per pair for the FX-72, and $999 per pair for the FX-74. In fact, they're still listed in pairs on AMD's price sheet today. If you go to buy 'em at Newegg, though, you'll find the CPUs priced and selling individually at a bit of a premium over list. Two FX-70s will set you back about $614, while two FX-72s are $820, and a couple of FX-74s total up to $1040. That's still not a bad price for the FX-70, relatively speaking, but then you have to take the $350 mobo into account. All told, the cheapest Quad FX mobo and processor combo will add $964 to your next Visa bill, while the most expensive one rings up just ten bucks short of $1400.

By contrast, quality mobos for Intel's quad-core processors can be had for under $180—well under, if you're not too concerned about high-end features like dual PCIe x16 slots. Probably the most apt comparison to the L1N64-SLI WS, if there is such a thing, is eVGA's version of the Nvidia nForce 680i SLI motherboard, which currently lists for $220. The combination of a Core 2 Quad Q6600 and this mobo costs $1066 at Newegg. Switching to a Core 2 Extreme QX6700 would raise the total to $1190 for the mobo and CPU.

None of these are exactly value products, but Quad FX systems wind up costing more than you might think, if you were to start with the AMD processor price list. Of course, the question of value becomes cloudy when talking about four-core rigs whose two main components add up to a grand or more. I should say right here, at the outset, that few of us really need four cores, especially since few of today's applications can really put 'em all to use at once. Glance over the test results in this article if you want to see that fact illustrated. We have now compiled a nice set of apps for our test suite, most of which can use four cores, but we had to dig a little bit to find them. So the results you're about to see are as much about potential as about what most folks would get out of a quad-core system today—something to keep in mind.